Which of the following steps are correctly sequenced in conventional water treatment? 1.Coagulation 2.Sedimentation 3.Filtration 4.Disinfection
- A1 → 2 → 3 → 4Correct
- B2 → 1 → 3 → 4
- C1 → 3 → 2 → 4
- D1 → 4 → 2 → 3
Solution
Concept
The chronological sequence of units in a conventional water treatment plant designed to transform raw water into safe potable water.
Step-by-step solution
Step 1: Coagulation involves the addition of chemicals (like alum) to raw water to neutralize charges on suspended and colloidal particles. Step 2: Sedimentation follows coagulation, where heavy flocs formed settle out of the water by gravity in sedimentation tanks. Step 3: Filtration removes the remaining fine suspended impurities and micro-organisms by passing water through beds of granular media (such as sand). Step 4: Disinfection is the final primary treatment step using agents like chlorine to destroy any remaining pathogenic bacteria and viruses.
Explanation
In a conventional water treatment plant, raw water first undergoes coagulation (where coagulants like alum are added to destabilize colloidal particles), followed by sedimentation (where the flocculated particles settle down), filtration (to remove remaining suspended impurities), and finally disinfection (to kill pathogenic microorganisms before distribution).
Why the other options are wrong
B: Sedimentation before coagulation is inefficient since particles will not clump effectively without coagulants. C: Filtration placed before sedimentation will quickly clog the filter beds. D: Disinfection cannot be the second step as organic matter and suspended solids must be removed first for it to be effective.
Shortcut
Remember the acronym CSFD: Coagulation → Sedimentation → Filtration → Disinfection.
Common mistake
Confusing filtration and sedimentation or placing disinfection before filtration, which would reduce filtration efficiency and fail to protect the filter media.
Correct answer: A) 1 → 2 → 3 → 4